1. Field of the Invention
The present invention relates to a color filter substrate for use in a color liquid crystal display apparatus and a display apparatus using the color filter substrate.
2. Description of the Prior Art
Liquid crystal display apparatuses have features such as small size, small thickness, low power-consumption and light weight, and therefore are widely used in various electronic equipment. In particular, active matrix liquid crystal display apparatuses including switching elements are widely adopted in office automation equipment such as personal computers, AV equipment such as television sets and portable information equipment such as cellular phones. In addition, in recent years, the size of liquid crystal display apparatus has rapidly increased and display quality of the apparatus such as definition, pixel effective area ratio (i.e., aperture ratio), viewing angle and color purity has been rapidly improved.
The liquid crystal display apparatus includes an active matrix substrate and a color filter substrate opposing to each other and also includes a liquid crystal layer sandwiched and held between these substrates.
The thickness of this liquid crystal layer is called a cell gap or a cell thickness and is defined in such a manner that plastic beads with a given size are sprayed onto the active matrix substrate or the color filter substrate and the plastic beads are sandwiched and held as spacers between the substrates.
In this method of spraying spacers, plastic beads are generally sprayed by airflow, so that the locations of the plastic beads cannot be identified. Accordingly, beads spacers distributed at random locations in a pixel cause scattering or transmission of light, so that the problem of degradation of display quality arises in the liquid crystal display apparatus.
In each of the active matrix substrate and the color filter substrate constituting the liquid crystal display apparatus, an in-screen display region in which a large number of pixels as minimum units of an image and an in-screen frame region located around the periphery of the in-screen display region are defined.
The liquid crystal display apparatus is mounted on a casing or a frame having an opening. The in-screen display region and the in-screen frame region are located in the opening and a portion surrounding the opening, respectively.
In the in-screen display region of the active matrix substrate, a plurality of gate lines and a plurality of source lines are arranged to be orthogonal to each other and a switching element is provided at each intersection between the gate lines and the source lines. A pixel electrode constituting a pixel is provided in each region surrounded with a pair of gate lines and a pair of source lines.
In the in-screen frame region of the active matrix substrate, extended lines of the gate lines and the source lines in the in-screen display region and auxiliary lines for defect correction or inspection are arranged. A light-blocking layer is provided on the entire in-screen frame region.
The in-screen frame region is not directly related to image display and includes a light-blocking layer for blocking light from a backlight or the like that is necessary for image display in the in-screen display region. If the light-blocking layer is made of a photosensitive resin, this layer needs to be thick in order to enhance the light-blocking property. In addition, in the case of mounting the liquid crystal display apparatus on a casing or a frame, the light-blocking layer in the in-screen frame region coincides with the portion surrounding the opening thereof, so that the light-blocking layer needs to be wide in consideration of a mounting margin.
Accordingly, if this light-blocking layer is provided in the in-screen frame region, a level difference occurs between the in-screen display region and the in-screen frame region, so that the cell thickness differs between these regions. This difference in the cell thickness causes a phase difference (retardation) in display light near the boundary between the in-screen display region and the in-screen frame region, so that color irregularities due to variation of a color tone might be perceived.
In view of this, to identify the locations of spacers and to suppress color irregularities occurring near the boundary between the in-screen display region and the in-screen frame region, a method of providing columnar spacers made of, for example, a resin on a color filter substrate was proposed.
In Japanese Patent Publication No. 8-114809, a technique of providing dummy spacers in the outside of an effective screen is disclosed. However, no preferable configuration and locations of the dummy spacers are specifically described.
In Japanese Patent Publication No. 10-82909, columns are formed on a peripheral portion of a substrate coated with a seal member so as to obtain the function of controlling a gap between the substrate and an opposed substrate (a color filter substrate.) However, no specific configuration of the columns is described.
In Japanese Patent Publication No. 2001-100221, a technique of forming spacers with a uniform thickness by utilizing a dry-film laminating process during formation of a color filter is disclosed.
In Japanese Patent Publication No. 2001-51266, a technique of providing spacers in an in-screen display region, an in-screen frame region and a non-display region at the outer periphery of the in-screen frame region is disclosed. However, no thickness relationship among the spacers is specifically described.